This invention relates generally to pollution control and the measurement and sampling of water effluent discharge and, more particularly, to a monitoring method and apparatus for measuring and sampling storm water run-off.
Growing concern over further pollution of rivers, streams, lakes and other bodies of water has given rise to more and stricter regulations governing the discharge and treatment of wastewater effluent. As a general rule, industrial run-off and municipal run-off are channeled through a sewer system for discharge into a large or flowing body of water. Depending on the flow rate and toxic material content of the run-offs, the effluent may require flow restraint and/or treatment before discharge. Continuous and relatively accurate monitoring and sampling of effluent run-off has thereby become essential.
In a typical sewer system, there is a substantially continuous stream of water flowing through an aqueduct, pipe or channel that is substantially horizontal. Streams of that type, known as open channel streams or flows, have long been monitored by a variety of methods and devices developed for that purpose. Examples of such known methods and devices may be found in U.S. Pat. Nos. 3,719,081, showing a flume arrangement and a pressure probe generating an electronic signal translatable into a flow rate; 3,929,017, showing a weir arrangement and a bubbler device responsive to the pressure required for gas bubbles to rise through a head of water; and 3,954,009 showing a float device associated with a weir arrangement. Weirs, flumes, and the like, are known as primary measuring devices and, as indicated in the said '017 patent, formulas have been developed for converting the height of liquid rise caused by the device into a flow rate based on the characteristics of the particular device.
Another primary measuring device is a plain cylindrical tube or pipe through which water flows in an open channel by gravity. That type of open channel flow is traditionally measured by the well known Manning formula wherein the slope of the hydraulic gradient is a factor so that the measured rate of flow is proportional to the slope of the pipe which normally will be some variance from the horizontal.
The various sensing devices and flow meters are known as secondary measuring devices which are adapted to automatically convert a sensed signal into a flow rate and also record the flow rate. The flow meters typically are programmable to the different types of primary measuring devices so that the proper conversion and flow rate is obtainable under varying flow conditions.
More recently, another source of potential water pollution has come under scrutiny, namely, storm water run-off. Storm sewers can be found in virtually all industrial facilities as well as commercial areas such as shopping malls and the like. The storm sewers are positioned and designed to be the collection point for storm water from building downspouts and paved or unpaved areas that require draining. Environmental Protection Agency (EPA) studies recently conducted have indicated that storm water run-off from urban and industrial sites carries a considerable amount of pollutants. As a result, the EPA has in late 1990 issued extensive regulations which apply to industrial and municipal storm water discharges.
As a general rule, storm sewers are remote from a main wastewater sewer system or wastewater treatment plant. Water flowing into a particular storm sewer thus must flow independently through its own drainage channel before it can be merged with and flow into the main sewer system. Understandably, the storm water run-off of a given individual location is intermittent, depending on weather conditions, and of greatly reduced volume compared to the wastewater discharge flowing in a main municipal storm sewer system. Since monitoring of individual storm sewers is often required by the EPA regulations, use of the described primary measuring devices like flumes and weirs for monitoring under such conditions is no longer practical or effective.
There thus exists a need for a flow rate measurement and sampling means for monitoring the run-off in an individual storm sewer. A device for achieving such monitoring should be simple to install in a storm sewer and yet provide sufficiently accurate results as required by regulations.